I. Field of the Invention
This invention relates to an immunoassay, and more particularly, this invention relates to an immunoassay of the type which utilizes the lysation of microcapsules such as red blood cells by complement activated by an antigen-antibody complex.
II. Description of the Prior Art
As a conventional immunoassay, radioimmunoassay (RIA) is known in which a specific antigen (or antibody) in a test sample is quantified utilizing the immunological reaction between antibody (or antigen) marked with radioisotope and the antigen (or antibody) in the test sample. However, since the radioisotope has to be determined, the equipment used for RIA is complicated and expensive. Further, several hours to several tens of hours are required for the accurate determination in RIA.
Enzyme immunoassay is also widely known as a conventional immunoassay. In this method, an antigen-antibody complex is obtained by the antigen-antibody reaction between antibody (or antigen) marked with an enzyme and antigen (or antibody) in a test sample. Thereafter, a specific antigen (or antibody) in the sample is determined utilizing the enzyme reaction of the marker enzyme. However, this method also requires several hours to several tens of hours for the accurate quantification of the antigen (or antibody).
As a method of quantifying complement in a serum, so called 50% hemolysis method (CH 50) developed by Meyer is known. In this method, sheep red blood cells sensitized with an optimum amount of hemolysin (anti-sheep red blood cell antibody) are reacted with a serum to be tested at 37.degree. C. for 60 minutes. In doing this, the sensitized sheep red blood cells are lysed by the action of complement in the test serum, so that the complement can be quantified by determining the degree of hemolysis. However, the hemolytic reaction can only be halted by cooling the reaction mixture in an ice bath. Further, in this method, the degree of hemolysis is determined by centrifuging the reaction mixture and measuring the absorbance at 541 nm of the supernatant obtained by the centrifugation. Thus, the procedure is time-consuming and further the test results are not always accurate.